Torque converters are commonly used to transfer drive torque from an engine to a transmission. A torque converter can provide torque multiplication, smooth ratio changing on acceleration, and good torsional vibration damping. Because a torque converter uses fluid coupling between its input and its output, there are inherent inefficiencies due to losses in the fluid. To realize better fuel economy, auto makers use a locking clutch, known as a torque converter clutch or TCC, to mechanically lock the input to the output to reduce losses at steady state speed conditions. In lower gears and at low vehicle speeds, the TCC cannot be locked because a locked drivetrain would pose drivability concerns. In order to strike a balance between vehicle drivability and fuel economy, systems have been developed that control the TCC to allow a small rotational speed difference, also known as slip, between the torque converter input and output. The technology of controlling a TCC to allow a controlled amount of slip is generally known as Electronically Controlled Capacity Clutch (ECCC).
Improvements in TCC slip control are desired to allow further improvements in vehicle drivability and fuel economy.